Re: does lactose made of alpha glucose n alpha galactose in our body?

Hi Candace,

As you probably already know, alpha- and beta- nomenclature is used to distinguish different stereoisomers of cyclical carbohydrate molecules (sugars). It is determined by whether the direction that the hydroxyl group on the first carbon (relative to the endocyclical oxygen - the oxygen in the ring) points axially (down, or alpha) or up (equatorially, or beta).

If you look at the structure of Beta-D-Lactose, which is the form we mostly talk about in biology, you'll note that the glycosidic bond between galactose and glucose is a beta-bond...so the galactose MUST be beta-galactose. However, the C1 carbon in glucose is far away from the glycosidic bond, so the glucose can be either alpha- or beta-glucose. What's interesting is that a process called mutarotation of that carbon allows for alpha- and beta- lactose to convert back and forth from one another...at equilibrium, a molecule of lactose in water at room temperature is 62.7% likely to be in the beta form, and 37.3% likely to occupy the alpha form.

I hope this has answered your question!

Billy.

PS - I got most of the information for this answer from a very, very specific book called "Dairy Chemistry and Biochemistry," which I checked out from my school's library. Despite being published in 1998 and purchased in 1999, I was still the very first person to have ever checked out the book.

Fox and McSweeney. "Dairy Chemistry and Biochemistry." Thompson Science. 1998. ISBN: 0-412-72000- 0